Subsea oil and gas production developments in recent years have been occurring in deeper water and thus entering more challenging offshore regions. Riser configuration designs are seeking to overcome numerous challenges such as highly dynamic offshore facility motions and environmental loadings, high top tension, and high hydrostatic pressure due to water depth. In practice, it has been demonstrated that in order to make deepwater large bore riser designs work, operators are frequently forced to utilize either very stable host topsides structures, e.g. spars, or more motion accommodating riser systems, e.g. freestanding hybrid riser (FSHR) systems. Both of these methods are currently used, but both of these methods have drawbacks. From a facility perspective, the use of a spar is not practical in some areas because of the lack of local export pipeline infrastructure. From a riser perspective, large bore risers encounter technical challenges as a result of the highly dynamic applications and sometimes do not meet strength and fatigue requirements. Existing deepwater riser systems such as FSHR have overcome dynamic application challenges by incorporating a flexible pipe jumper into the system design. However, this is a quite expensive solution due to system complexity and the installation requirements. In some instances, a design alternative to overcome technical and commercial challenges is to use a flexible pipe for the entire riser system. A particular challenge is the flexible pipe inner diameter limitation with increasing hydrostatic pressure resulting from increased water depth increasing the risk of collapse. In projects requiring large inner diameter risers, this may result in an increased riser count with smaller diameters if flexible pipe is being used, or it may completely eliminate flexible pipe as a riser option. Increased riser count requires multiple hang off slots on the topside structure, seabed congestion and results in capital expense increase.
There exists a need for motion accommodating riser systems useful in deepwater oil and gas developments which would avoid the above mentioned challenges with existing flexible pipe riser systems.